THE HAND-ARM SYSTEM FATIGUE ASPECTS IN PRODUCTION LINES.

WHAT TO KEEP IN MIND WHEN USING HAND-HELD SCREWDRIVERS.

When it comes to hand-arm system fatigue due to the use of hand tools and specifically screwdrivers, there are multiple important aspects to keep in mind.

In addition to the necessary evaluations regarding the choice of the screwdriver in terms of vibration and noise, torque and power, and its geometry/weight, it has to be said that fatigue to operators is most often due to improper methods of use and especially to the inappropriate choice of the type of grip with respect to the position of the tightening points.

Unfortunately, improper use of screwdrivers is often observed in production lines, and this is to the detriment of the operator’s entire hand-arm system.

Let’s have a brief focus specifically on the proper ways for the operator to use the screwdriver and the choice of “grip” depending on the area of operation.

The key points for the operator’s manual grip are these:

• Straight-grip screwdrivers: to avoid straining wrist positions, it is advisable to use straight-grip screwdrivers only when the tightening points are on horizontal surfaces.

• Pistol grip screwdrivers: the pistol grip screwdriver is suitable for operating points placed on vertical planes. The wrist position with pistol grip screwdrivers is correct when the tightening points are placed between elbow height and shoulder height.

To avoid incongruous wrist postures and movements resulting in fatigue, it is advisable to use tools in which the direction of the handle allows the wrist to maintain a nearly straight position.

Maintaining a good wrist position ensures a reduction in the use of force.

• Inverted pistol grip screwdrivers: the use of inverted pistol grip screwdrivers is indicated when we have operating points placed on vertical planes, within cavities unreachable by traditional screwdrivers (e.g., in oven assembly); in this case the wrist position is correct when the tightening points are placed at or below elbow height.

In summary, it can be stated that:

• Tightening points placed at or above shoulder height are to be avoided because they are easy causes of the onset of shoulder tendinitis

• When designing a workstation, it is important to ensure that the tightening points are kept about elbow height and the arm and as close to the body as possible in both standing and sitting positions.

• When choosing pistol grip screwdrivers, prefer the more versatile ones that provide pneumatic or electric power from several points so that cable constraints do not hinder operation and result in the operator adopting incongruous wrist movements and consequent fatigue.

If, on the other hand, we want to switch to a mechanical grip, i.e., the aid of reaction arms or other ergonomic devices that “prevent the operator from misusing screwdrivers” this proves to be an excellent strategy. In fact, the operator finds the screwdriver bracketed on the arm in the proper position with respect to the bench and the component, and thus, in addition to preventing improper use, the characteristics of the tool such as weight/reaction on the hand/vibration/heating and the difficulties of using the tool such as, for example, retrieving the tool on the bench, positioning and centering the screwdriver on the workpiece are eliminated at the source.

In conclusion, it should then always be remembered that Training on the Correct Use of Equipment is a fundamental and indispensable activity for operators.

Fiam has also recently updated its eTensil range of electrical solutions with pistol grip screwdriver ranges. Find out all their features on our website: https://www.fiamgroup.com/en/prodotti/pistol-electric-screwdrivers/

If you would like to learn more about other topics on workstation ergonomics our ebook is available and you can request it by clicking the link below for more information.